The present invention relates to a fuel supply system for internal combustion engines, including a fuel delivery pipe.
In a conventional fuel supply system for internal combustion engines in which fuel injectors are supplied with fuel from a delivery pipe, air is mixed with fuel in the fuel delivery pipe for some reason or fuel vapor is generated under high temperature condition. Such air or fuel vapor is purged to a return piping through a pressure regulator when a fuel pump is in operation. For example, Japanese Laid-open utility Model No. 62-137379 discloses a fuel supply system, wherein a fuel pipe connected to the fuel delivery pipe is provided thereabove and is connected to the pressure regulator so that the air or vapor is purged to the return piping without being accumulated in the fuel delivery pipe.
It is desired to eliminate the return piping in order to simplify the fuel supply system. However, if the return piping is eliminated there is no way for air or vapor in the fuel delivery pipe to be purged and it is accumulated in the fuel delivery pipe, resulting in decrease of fuel amount to be injected.
Further, in conventional fuel supply systems such as disclosed in Japanese Laid-open Patents Nos. 56-81230, 60-147548 and 2-5723, fuel injection amount is increased until vapor or air in the fuel is purged completely.